The prevalence and associated factors for glucose intolerance among Saudi populations in urban and rural communities were investigated among 13 177 subjects, 15 years and over, from different regions of Saudi Arabia. The data were standardized using the known age structure of the Saudi population. The sample was randomly selected from subjects who participated in the National Epidemiological Household Study for Chronic Metabolic Diseases. Medical and social history was ascertained from all the study population during house visits. All subjects were then requested to attend a local primary care centre for physical examination and phlebotomy for measurement of random plasma glucose (RPG). A 75 g oral glucose tolerance test was employed for subjects with borderline values. WHO criteria for diagnosis of diabetes mellitus (DM) and impaired glucose tolerance (IGT) were applied. Mean RPG from the urban population was significantly higher than in the rural population. Age adjusted prevalence of DM was significantly higher in the urban population (males 12 %, 95 % CI 11-13 and females 14 %, 95 % CI 13-15) than in the rural population (males 7 %, 95 % CI 7-8 and females 7.7 %, 95 % CI 7-9) and is among the highest in the world. The prevalence of DM increased with age. The lowest and highest prevalences of DM in the urban population were 2 % for subjects aged 15-20 years and 49 % for female subjects aged 51-60 years. The lowest and highest prevalences of DM among rural population were 1 % for subjects aged 15-20 years and 29 % for female subjects over the age of 60 years. Fifty-six per cent of diabetic patients were newly diagnosed at the time of the study. Age adjusted prevalence of IGT was not significantly higher in the urban population. The highest prevalence of obesity, BMIΟΎ30, was among urban female subjects. Age, obesity, and family history of DM were associated with DM. Considering the young nature of Saudi population, the prevalence is expected to increase in the near future. There is a need to develop a multi-disciplinary approach for the general population with special attention to female subjects for prevention through controlling modifiable risk factors such as obesity and sedentary life style, improving glycemic control of the diabetic population, and early identification and treatment of diabetic complications.